Thermoforming

Elium, the first welding. The composite parts made from Elium resin can be developed and recycled by thermoplastic resin is designed for the manufacturing composite material parts with certain mechanical properties similar to that of thermosetting. The uniqueness of Elium is it behaves as a thermoplastic which is designed for thermoforming, recycling and depolymerization. The principle involved is coarsely crushing Elium resin and then heat depolarized as it can be recovered and purified into a resin with the similar properties as that of the virgin resin. Elium resin is a tremendous asset, especially in the manufacturing of wind turbines where non- recyclable epoxy resin is used in the manufacturing of blades

Elium, the first welding. The composite parts made from Elium resin can be developed and recycled by thermoplastic resin is designed for the manufacturing composite material parts with certain mechanical properties similar to that of thermosetting. The uniqueness of Elium is it behaves as a thermoplastic which is designed for thermoforming, recycling and depolymerization. The principle involved is coarsely crushing Elium resin and then heat depolarized as it can be recovered and purified into a resin with the similar properties as that of the virgin resin. Elium resin is a tremendous asset, especially in the manufacturing of wind turbines where nonrecyclable epoxy resin is used in the manufacturing of blades.

A temperature and strain rate dependent model for the thermoforming process of amorphous polymer materials is proposed. The polymeric sheet is heated at a temperature above the glass transition temperature then deformed to take the mold shape by the means of an applied pressure. The applied process temperature is taken uniform throughout the sheet and its variation is due only to the adiabatic heating. The behavior of the polymeric material is described by a micromechanicallybased elastic-viscoplastic model. The simulations are con-ducted for the poly(methyl methacrylate) using the finite element method. The polymer sheet thickness and the orientation of the polymer molecular chains show an important dependence on the process temperature, the applied pressure profile, and the contact forces with the mold surface.

Stress whitening problem in thermoformed alumina trihydrate (ATH) reinforced poly(methyl methacrylate) (PMMA) was studied. In situ heavy-gage thermoforming of acrylics was entirely replicated under laboratory controlled conditions at different operation parameters. Samples were monitored with optical microscope after the completion of the thermoforming operation. For stress whitening quantification, a new index was proposed from image histograms of processed optical micrographs. Results indicated that stress whitening in PMMA/ATH samples increases with level of plastic deformation at all thermoforming conditions. The influence of the forming rate and forming temperature on the degree of stress whitening was explained in terms of change in material behavior and microdeformation mechanisms around two characteristic temperatures of PMMA/ATH. Developed method for stress whitening quantification characterizes different levels of stress whitening with single numeric values. It is shown that stress whitening index and density of microdeformation features display a strong correlation. Higher density of particle cracks at low forming temperatures results in higher stress whitening levels. Increased surface irregularity and large size voids at high forming temperatures produce lower stress whitening.

Dans cet article nous nous intéressons, d'une part,à la caractérisation biaxiale, en soufflage libre du comportement viscoélastique des membranes thermoplastiques circulaires et amorphes, et d'autre part,à la simulation numérique de thermoformage. La membrane thermoplastique utilisée est l'ABS (Acrylonitrile butadiène styrène). Pour l'identification du comportement du thermoplastique, nous considérons le modèle intégral de Lodge. Dans un premier temps, nous utilisons la méthode des différences finiesà pas variables pour la résolution du problème d'équilibre de la membrane et, ensuite, un algorithme modifié de Levenberg-Marquardt pour minimiser la différence entre la pression calculée et celle mesurée. Ceci permet l'identification des constantes matérielles incorporées dans le modèle utilisé. Pour la simulation numérique de thermoformage, nous considérons la MEF en dynamique explicite et une charge en débit d'air qui obéità l'équation d'état de Redlich-Kwong des gaz réels. Pour cela, nous adoptons une formulation lagrangienne et l'hypothèse de la théorie des membranes. Le code paréléments finis résultant, nous a permis d'étudier, en thermoformage, l'influence de la loi de comportement sur la distribution finale desépaisseurs et des contraintes dans une pièce en ABS.

Stress whitening problem in thermoformed alumina trihydrate (ATH) reinforced poly(methyl methacrylate) (PMMA) was studied. In situ heavy-gage thermoforming of acrylics was entirely replicated under laboratory controlled conditions at different operation parameters. Samples were monitored with optical microscope after the completion of the thermoforming operation. For stress whitening quantification, a new index was proposed from image histograms of processed optical micrographs. Results indicated that stress whitening in PMMA/ATH samples increases with level of plastic deformation at all thermoforming conditions. The influence of the forming rate and forming temperature on the degree of stress whitening was explained in terms of change in material behavior and microdeformation mechanisms around two characteristic temperatures of PMMA/ATH. Developed method for stress whitening quantification characterizes different levels of stress whitening with single numeric values. It is shown that stress whitening index and density of microdeformation features display a strong correlation. Higher density of particle cracks at low forming temperatures results in higher stress whitening levels. Increased surface irregularity and large size voids at high forming temperatures produce lower stress whitening.

A temperature and strain rate dependent model for the thermoforming process of amorphous polymer materials is proposed. The polymeric sheet is heated at a temperature above the glass transition temperature then deformed to take the mold shape by the means of an applied pressure. The applied process temperature is taken uniform throughout the sheet and its variation is due only to the adiabatic heating. The behavior of the polymeric material is described by a micromechanically-based elastic-viscoplastic model. The simulations are conducted for the poly(methyl methacrylate) using the finite element method. The polymer sheet thickness and the orientation of the polymer molecular chains show an important dependence on the process temperature, the applied pressure profile, and the contact forces with the mold surface. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Plastics have been highly successful in replacing such conventional materials as metals, glass, and wood in a wide variety of applications due to their special property advantages such as high strength-to-weight ratio, corrosion resistance, versatility of part design, and ease of fabrication. The various plastic products are formed by processing polymers by one of the number of available techniques such as injection molding, compression molding, blow molding, profile extrusion, and sheet extrusion followed by stamping or thermoforming. In all these processes, the molten polymer is subjected to a wide range of shear rates and temperatures. During deformation, viscous heat is dissipated due to the friction between the highly viscous polymer melt and the various parts of the processing equipment that it comes in contact with. The viscous heat dissipated leads to a temperature rise, resulting in an offset of the setting of the extruder temperature profile with respect to throughput rate or screw speed. For all high output rate operations, it is essential to know the viscous heat generated in order to appropriately design the conventional extruder screw so as to minimize the temperature increase in the process of plastication and to optimize the extruder temperature profile with respect to the throughput rate or screw speed. Viscous heat estimation is also critical when processing heat- sensitive polymers so as to maintain the melt temperature well below the degradation point.

The oxygen transmission rate (OTR) of packaging materials used for modified atmosphere packaging (MAP) of chilled products varies extensively with temperature, relative humidity (RH) and material thickness after the thermoforming of packages. Two different polymer combinations were studied: APET/PE (tray) and PA/PE (lid). A temperature reduction of 8°C (in the interval 7-23°C) caused an OTR reduction of 26-48% depending on material type, degree of thermoforming and RH. A 2-3-fold increase in OTR was observed for PA/PE film when measured at 100/100% RH compared to 0/100% RH, whereas the APET/PE trays were not affected by RH. Increased OTR was observed as a result of material thinning; however, the increase was not always directly proportional to the degree of material thinning. Even very small amounts of oxygen have, in combination with light exposure, significant effects on oxidative quality deterioration of many products. Consequently, the changes in OTR observed in this study emphasize the necessity of evaluating the performance of packaging materials under realistic storage conditions, in order to estimate the real oxygen content of a chosen package solution. The light transmission through the packaging material was found to be reduced to 0-30% (300-800 nm) by dyeing of the lid and/or addition of labels. Thus, it is easy to protect the products from light, at least partly. Copyright

This study describes in detail the mechanical properties of polymethylmethacrylate (PMMA) denture base resins with regard to fabrication procedures, moulding and thermoforming. The investigation included eight specimens of each group of the materials, made separately for each experimental protocol (moulding and thermoforming). Analysis of the mechanical properties of the tested resins was comprised of tensile and 3-point bending strengths, elongation, fracture toughness and micro-hardness tests. Data obtained from the mechanical tests were statistically processed by using one-way analysis of variance (ANOVA) with Tukey's post-hoc test and with the significance level α=0.05. Triplex cold specimens showed the lowest bending strength, fracture toughness and micro-hardness as well the highest standard deviations. Biocryl C in a thermoformed condition exhibited higher tensile and bending strength in comparison to the same material but in the as-received condition (before thermoforming), while the results are opposite for fracture toughness and micro-hardness. Compared to Triplex hot, thermoformed Biocryl C had statistically non-significantly higher values for bending strength and micro-hardness, but significantly lower ones for fracture toughness and tensile strength. In contrast, the lowest dissipation of testing results in all mechanical tests was recorded for Biocryl C fabricated by a thermoforming process, meaning that this material has the highest predictability of the materials tested. The mechanical properties of thermoformed PMMA materials are comparable to cold and hot polymerized PMMA materials. Standard deviations obtained for thermoformed PMMA material are lower than those obtained with cold and hot polymerized PMMA materials.

In this study, sandwich panels were fabricated with neat and nanophased foam cores and 3-layered plain weave carbon fabric/SC-15 epoxy-nanoclay composite face sheets. Neat and nanophased foam cores with Nanocor Ò I-28E nanoclay at a loading of 0.5% and 1% by weight were prepared. Sandwich panels were then fabricated using co-injection resin transfer molding process. The facesheets were made by infusing SC-15 epoxy containing 1% and 2% by weight of nanoclay into 3 layers of plain weave carbon fabric. Samples of size 100 • 100 mm were then cut from the panels and subjected to low-velocity impact loading using an instrumented impact test setup. Impact response of the samples was recorded and compared. The tested samples were then sectioned into two halves and scanned using a scanner, optical and scanning electron microscopes to understand the failure patterns. Samples with nanophased foam sustained higher loads and had lower damage areas as compared with neat counterparts. Nanophased foam cores exhibited brittle fracture.

This work reports the effects of thermoform molding process conditions on polyvinylchloride (PVC) and polyethylene (PE) double layer package materials. Mechanical and microstructural properties of the package material were examined by different test methods which are tensile properties, tear resistances and scanning electron microscopy (SEM). Furthermore, package materials, which are produced in different conditions by thermoform molding. Effect of different mold depths and process temperatures on the samples are determined by thermal aging process at 608C in first, third, and seventh days. With increase in mold depth from 25 mm to 75 mm, there is a significant increase in tensile strength from 45 MPa to 55 MPa, thermoform temperature at 1508C. The highest elongation of the material was obtained thermoform temperature at 1658C as 80%, mold depth at 35 mm. Tensile strength and elongation (%) of the material generally decrease by aging time with changing of mold depth (25, 35, and 75 mm) of the double layer package material. In addition, tear resistances of the material decrease via aging time in various thermoform temperatures (1508C, 1658C, and 1758C) due to the orientation of the segments. Scanning electron microscopic (SEM) images of the materials were taken for aging process in first, third, and seventh days.

The purpose of this article is to review the publications dealing with the application of finite elements in the thermoforming process. Although no attempt has been made to discuss the theoretical aspects of these publications, their general methodologies have been presented. The paper is particularly aimed at readers who are seeking an ovcrall view of the subject and possibly interested in acquiring a CAD system for thermoforming technology.

The forming or draping of a textile composite preform may result in large changes in the ®brous microstructure of the preform. This change in the local ®ber orientation leads to signi®cant changes in the fabric permeability as well as the mechanical properties of the ensuing composite structure. Therefore, this change in orientation of the tows of the preform needs to be known accurately to calculate the various eective properties of the composite. A new ®nite element approach for stamping analysis of a plain-weave textile composite preform has been developed. This model is simple, ecient and can be used in the existing ®nite element codes. The model represents the preform as a mesh of 3-D truss elements and 3-D shell elements. The truss elements model the tows, which are allowed to both scissor and slide relative to one another. The shell elements represent a ®ctitious material that accounts for inter-tow friction and ®ber angle jamming. The model takes into account large strains and large deformations. In-plane uniaxial tension tests have been performed on plain-weave specimens for determining the constitutive law of the transforming medium and to show the inter-tow sliding. Application of the model is demonstrated by simulating the stamping of a preform by a spherical punch. The results from the simulation show good correlation with results from the experiments. Ó

The forming or draping of a textile composite preform may result in large changes in the ®brous microstructure of the preform. This change in the local ®ber orientation leads to signi®cant changes in the fabric permeability as well as the mechanical properties of the ensuing composite structure. Therefore, this change in orientation of the tows of the preform needs to be known accurately to calculate the various eective properties of the composite. A new ®nite element approach for stamping analysis of a plain-weave textile composite preform has been developed. This model is simple, ecient and can be used in the existing ®nite element codes. The model represents the preform as a mesh of 3-D truss elements and 3-D shell elements. The truss elements model the tows, which are allowed to both scissor and slide relative to one another. The shell elements represent a ®ctitious material that accounts for inter-tow friction and ®ber angle jamming. The model takes into account large strains and large deformations. In-plane uniaxial tension tests have been performed on plain-weave specimens for determining the constitutive law of the transforming medium and to show the inter-tow sliding. Application of the model is demonstrated by simulating the stamping of a preform by a spherical punch. The results from the simulation show good correlation with results from the experiments.

Controlled atmospheric pressure resin infusion (CAPRI) is a variation of the vacuum-assisted resin transfer molding (VARTM) process. The CAPRI process increases the fiber volume fraction of the preform prior to infusion via debulking and applies a reduced pressure gradient during infusion to minimize thickness gradients during processing. This study experimentally investigates the effect of debulking and reduced pressure gradient on the incoming material parameters, process behavior and final dimensional tolerances. The effect of debulking on fabric permeability and compaction behavior has been investigated and shows a significant impact on the infusion time and final fiber volume fraction. Several E-glass plain weave preforms have been infused and flow, pressure and thickness data has been recorded and compared to traditional VARTM processing. A previously developed model uses the experimentally obtained permeability data and good agreement of the flow behavior is observed, the CAP...

In this study, 5% and 15% in weight carbon fiber reinforced polypropylene (PP) sheets were formed under appropriate vacuum and temperature conditions by using truncated cone-shaped thermoforming mold. In addition to this, 5% in weight glass fiber reinforced High Density Polyethylene (HDPE) sheets were formed using truncated cone-shaped, cylindrical, and cubic shaped thermoforming molds by thermoforming. Composite sheets used in this work were produced with a laboratory-type plastic extruder which has a screw diameter of 50 mm. In production of HDPE composite sheets, as a reinforcing material, chopped glass fibers (E-glass) which were provided from glass fiber manufacturer SISECAM A.S. Company were used. Using the same procedure PP (Borealis BE50-7032) thermoplastic granules were used as a matrix material in production of carbon fiber composite sheets. In carbon fiber reinforced sheets, chopped fibers were added during manufacturing. After thermoforming, composite semi-products were ...

The problem of modeling and the quasi-static finite element simulation of thermoforming processes for viscoelastic sheet is considered. To take account of the enclosed gas volume, responsible for inflation of the thermoplastic membrane, which contributes significantly to the strength and stiffness of a thermoplastic structure, the expression of external virtual work is expressed by a closed volume integral. The pressure load used in modeling is thus deduced from the thermodynamic law of ideal gases. The viscoelastic behavior of the Lodge model is considered. The Lagrangian formulation together with the assumption of the membrane theory is used in the finite element implementation. The numerical validation is performed by comparing the theoretical solution for the uniaxial and equibiaxial hencky deformation and free inflation with numerical results. Moreover, the influence of the Lodge constitutive model on the thickness and stress distribution in the thermoforming of containers made of HIPS is presented.

The problem of modeling and the dynamic finite element simulation of thermoforming process for viscoelastic sheet are considered. The pressure load used in modeling is thus deduced from the thermodynamic law of ideal gases. The viscoelastic behavior of the K-BKZ model is considered. The Lagrangian formulation together with the assumption of the membrane theory is used in the finite element implementation. The numerical validation is performed by comparing the theoretical solution for the uniaxial and equibiaxial hencky deformation with numerical results. Moreover, the influence of the K-BKZ constitutive model, for three linear time distribution of airflow rate loading, on the thickness and on the stress distribution in thermoforming of containers made of HDPE are analyzed. POLYM. ENG. SCI., 45:1319 -1335, 2005. © 2005 Society of Plastics Engineers

The objective of this work was to obtain, through a simple experimental assembly, the real influence of the friction and process conditions in the assisted thermoforming process. The use of simulation tools to optimize this process requires the knowledge of the sheet-plug system friction coefficient [l], the used temperature and velocity conditions, and due to that, the software does not have a wide database. For this, the users suppose l with the previous known difference between the simulated and the experimental data. For this reason, the obtaining of l may allow to achieve more accurate simulations. In this work, a modified pendulous impact in Izod geometry was used to the measurements. The l increased with the sheet temperature. On the other hand, it was not possible to detect a significant l variations regarded with the plug material.

ABSTRACT Biocomposites from renewable resources have been attracting increasing attention over the last two decades, mainly for two major reasons: first, environmental concerns, and second, the realization that our petroleum resources are finite. Nowadays, biofiber-reinforced composites are seen as potential materials for many engineering applications. Unfortunately, there are still issues that limit their future applications including long-term performance and processing variability. This article gives an overview of the wide variety of biocomposite processing techniques as well as the factors (moisture content, fiber type, content as well as coupling agents, and their influence on composites properties) that affect the processes. Before processing biocomposites, semifinished product manufacturing is also a vital part, which is illustrated. Processing technologies for biofiber-reinforced composites are discussed on the basis of the thermoplastic matrix (compression molding, extrusion, injection molding, LFT-D method, and thermoforming) and thermosets (resin transfer molding, sheet molding compound) as well as other implemented processes, that is, thermoset compression molding and pultrusion. Furthermore, we include comparative studies between different processes regarding the biocomposites' structure–property relationships.Keywords:biofiber-reinforced plastic composites;moisture;fiber type;coupling agent;extrusion;injection molding;compression molding;thermoplastics;thermosets;pultrusion;thermoforming;resin transfer molding;sheet molding compound;LFT-D method

This work reports the effects of thermoform molding process conditions on polyvinylchloride (PVC) and polyethylene (PE) double layer package materials. Mechanical and microstructural properties of the package material were examined by different test methods which are tensile properties, tear resistances and scanning electron microscopy (SEM). Furthermore, package materials, which are produced in different conditions by thermoform molding. Effect of different mold depths and process temperatures on the samples are determined by thermal aging process at 60°C in first, third, and seventh days. With increase in mold depth from 25 mm to 75 mm, there is a significant increase in tensile strength from ∼45 MPa to ∼55 MPa, thermoform temperature at 150°C. The highest elongation of the material was obtained thermoform temperature at 165°C as 80%, mold depth at 35 mm. Tensile strength and elongation (%) of the material generally decrease by aging time with changing of mold depth (25, 35, and 7...

In this study, 5% and 15% in weight carbon fiber reinforced polypropylene (PP) sheets were formed under appropriate vacuum and temperature conditions by using truncated cone-shaped thermoforming mold. In addition to this, 5% in weight glass fiber reinforced High Density Polyethylene (HDPE) sheets were formed using truncated cone-shaped, cylindrical, and cubic shaped thermoforming molds by thermoforming. Composite sheets used in this work were produced with a laboratory-type plastic extruder which has a screw diameter of 50 mm. In production of HDPE composite sheets, as a reinforcing material, chopped glass fibers (E-glass) which were provided from glass fiber manufacturer SISECAM A.S. Company were used. Using the same procedure PP (Borealis BE50-7032) thermoplastic granules were used as a matrix material in production of carbon fiber composite sheets. In carbon fiber reinforced sheets, chopped fibers were added during manufacturing. After thermoforming, composite semi-products were ...

The chemical, mechanical, and electrochemical attributes of the Parylene sheath electrode (PSE) were evaluated following a post-fabrication thermoforming process to determine its impact on both the polymer and thin film platinum materials. The three-dimensional conical shape of the PSE was formed via thermal molding of a surface micromachined Parylene C microchannel using a custom shape-forming microwire having the desired taper at 200°C for 48 hours under vacuum. Contact angle and Fourier transform infrared spectroscopy measurements indicated that the thermoforming process resulted in no significant changes to the surface and bulk chemistry of Parylene. The thermoformed Parylene samples possessed greater <RXQJ ¶V PRGXOXV EXW retained their flexibility. Electrochemical characterization of electrodes before and after thermoforming revealed a decreased storage charge capacity and increased electrode impedance, however, recording functionality was not lost as resolvable neuronal unit activity was successfully obtained post-implantation.

This article presents an experimental investigation carried out to understand the mechanical behavior of composite materials made of 3D stitched wovenknitted basalt fabrics. The innovative preforms used consist of two outer layers of a plain woven fabric combined with two inner layers of weft-knitted fabrics. The weft-knitted fabrics selected for the study were varied plain knit, 1 Â 1 rib, Milano, and interlock. The fabric layers were stitched together with Kevlar yarns. These 3D stitched preforms were impregnated with polyester resin using resin transfer molding, and the corresponding composites obtained were tested under tensile, bending, and impact loads. The results obtained show that the type of knitted structure significantly influences the mechanical performance of the 3D stitched woven-knitted composites. The composite using interlock structure as the inner layers has the best results concerning energy absorption and tensile strength. The varied plain knit structure has proved to be the best suited to impart stiffness as it provides the highest Young's modulus among the above four knitted structures.

Thermo-mechanical behaviors of thin thermoplastic sheets under thermoforming conditions are generally studied in the frameworks of hyperelasticity and large deformations. The boundary conditions of the mechanical problem which represents the shaping operation are defined by the clamping configuration of the free edges of the sheet. By heating a flat thermoplastic sheet of totally or partially constrained edges during a thermoforming process, incontrollable changes of the initial boundary conditions manifest by buckling and warpage. Without consideration of the real process conditions, the mechanical problem risks to be ill posed. The current study focuses on representative unidirectional stretching tests under isothermal conditions conducted on high impact polystyrene (HIPS) specimens with free lateral edges. The aim is to identify the parameters of the Mooney-Rivlin hyperelastic model which is generally admitted in the case of the HIPS for temperatures above the glass transition. To measure the non-negligible out-of-plane deformations which manifest during the stretching operation, a hybrid numerical-experimental approach is introduced. This approach combines kinematic fields measured by the stereo digital image correlation (stereo-DIC) technique and a finite element model updating (FEMU) procedure. First, a dataset of displacement fields measured during stretching tests at controlled temperatures and strain rates is constructed. Second, sequential quadratic programming (SQP) based inverse identification procedure is implemented to minimize an objective function which combines the experimental and numerical displacement fields. A case of study is presented to test the limits of the hybrid numerical-experimental approach under incremental stretching levels. The optimization results indicate that the extent of the kinematic fields compared to the effective size of the tested specimen and the excessive stretching of the stereo-DIC speckle are the major limits to the applicability of the approach. The conducted study constitutes a preliminary step towards more accurate consideration of real boundary conditions to simulate thermoforming of thin thermoplastic sheets.

In this work, we are interested in numerical simulation in free and confined inflation of a thin, isotropic and incompressible thermoplastic membrane, using the dynamic finite element method. Inflation of the membrane is controlled by the gas equation of state flowing into the enclosed volume. The dynamic pressure loading used in modeling is thus deduced from one of the three equations of state: the Redlich-Kwong, the van der Waals and the ideal equations. The viscoelastic behavior of the Lodge model is considered. The Lagrangian formulation, together with the assumption of the membrane theory, are used. The effect of the gas on the thickness and stress distribution, for the free and confined inflation (thermoforming process), is analyzed for these three gas equations of state.

An innovative shielding concept to reduce radiated emissions from components and tracks on printed-circuit boards is proposed. The new shield is made of a polycarbonate foil, which is coated by a thin film of nickel (only 50 nm in thickness) and by a 5-m thick layer of tin, and successively thermoformed. The innovative characteristics of such a high-technology shield are the extremely light weight, the high thermoformability, good shielding performance against both far-field and near field sources, low production costs, low installation costs, minimum occupied volume. The mechanical, chemical, and electromagnetic performance of the new shield has been characterized experimentally. Different bonding solutions are tested in order to optimize the shielding performance of the screening cover installed on a conductive ground plane.